In a dutch oven or soup kettle over medium heat, saute onion and carrots in butter for 5 minutes, stirring occasionally. Add squash, broth, zucchini, salt, thyme and pepper; bring to a boil. Reduce heat; cover and simmer until vegetables are tender, about 30 minutes. Cool until lukewarm. In a blender or food processor, puree soup in small batches until smooth; return to kettle. Add cream and milk; mix well and heat through (do not boil). Garnish with parmesan cheese, if desired. 12-14 servings.

(I have omited the cream in this, and it turned out great--with less calories).